A fastening device disclosed in Japanese Utility Model Application Laid-Open No. S61-20873 comprises a support metal piece secured to one body to be fastened, a base metal piece secured to the other body to be fastened, and an operating lever having a U-shaped configuration in section. A basal end part of the operating lever is turnably connected to the base metal piece through a first shaft. The fastening device further comprises an arm, one end part of which is removably and turnably connected to the support metal piece through a second shaft and the other end part of which is turnably connected to the basal end part of the operating lever through a third shaft. The arm is comprised of an assembly which includes two elongate arm elements each provided at one end thereof with a engaging part, and a compression coiled spring. The second and third shafts are biased toward each other by the compression coiled spring.
In the above fastening device, a dead point where the third shaft is aligned with the first and second shafts is located at an intermediate of the turning range of the operating lever. The operating lever is turned beyond the position where the third shaft is located at the dead point and overlapped with the base metal piece. In that condition, the two bodies are fastened. The overlap position where the operating lever is overlapped with the base metal piece is kept by a lock mechanism.
The lock mechanism will now be described. A cutout is formed at one side wall of the operating lever, and one part of the peripheral edge of this cutout is provided as a lock claw. Two support elements are cut and raised on the base metal piece, and a lock pin is laid between the two support elements. One end part of the lock pin is inserted in a support hole of one support element with play such that the lock pin is turnably supported by the support element. The other end part of the lock pin is passed through a long hole of the other support element and provided as a handle part.
A hook pin is secured to the base metal piece at the area on the opposite side of the third shaft when viewed from the lock pin. A tension coiled spring (pin biasing member) is hooked over between this lock pin and the hook pin. In the state that the operating lever is overlapped with the base metal piece as mentioned above, the lock pin is biased by the tension coiled spring and is kept engaged with the lock claw of the operating lever. When the handle part of the lock pin is moved along the long hole of the support element against the tension coiled spring, the lock pin is disengaged from the lock claw and brought to the engagement released position. With the lock pin kept in the engagement released position, the operating lever is turned in such a manner as to be moved away from the base metal piece and the operating lever is further turned until the third shaft is moved beyond the dead point. By doing so, the two bodies are released from the fastened condition.
However, in the device disclosed in the above-mentioned Laid-Open Publication, when the operating lever is located away from the base metal piece, the tension coiled spring installed on the base metal piece is exposed. Therefore, there is such a risk that the tension coiled spring is accidentally contacted with the operator's hand and broken or disengaged from the lock pin. Moreover, since it is necessary to keep the lock pin in the engagement released position with one hand and to turn the operating lever with the other hand simultaneously at the time of unfastening operation, operability is bad.